Low Electric Field Regime Research Articles

Erratum to: Influence of Processing Conditions and Material Properties on Electrohydrodynamic Direct Patterning of a Polymer Solution

An electrohydrodynamic (EHD) patterning method was utilized to obtain high-resolution line patterns in a low electric field regime without an additional mechanical drawing process. Molecular weight and weight percent of a polymer were selected as key parameters to reduce the voltage. EHD patterning was performed using polyethylene oxide (PEO) solutions. The threshold voltages (V th) to initiate jet ejection are almost the same for all solutions. A method verified in this study, reducing the driving voltage (V d) just after the initiation of the jet at the threshold voltage, can make a very thin, continuous jet, while increasing molecular weight and weight percent were enabled to further reduce the input voltage. As the voltage reduction ratio (V d/V th) is decreased, the jet behaves like a solid rather than a liquid due to its fast solidification. The line width of the resultant line pattern could be tuned from 50 nm to 10 μm depending on the substrate moving speed. Contour maps were also developed that show the pattern mode variation as a function of the voltage reduction ratio and key parameters. The results show that well-defined PEO line and grid patterns can be fabricated via the proposed EHD direct patterning under appropriate conditions.

Identification of current transport mechanism in Al2O3 thin films for memory applications

The effect of oxygen anneal on the electrical characteristics, especially on the current transport mechanism, of Al2O3 films in the thickness range of 10–30 nm was examined in detail. The analyses were performed at electric fields of ≤2.5 MV/cm to effectively address the reliability of Al2O3-based devices operating in the low electric field regime. The general conduction mechanism equations were used to simulate the expected current density (J) values for a given electric field (E) range. The characteristic linear plots of the conduction mechanisms were then used to compare the experimental and simulated data to identify the most probable mechanism occurring in the dielectric. Parameters like barrier height and activation energy were extracted from the fit. It was found that oxygen anneal has profound effects on the electrical properties of Al2O3 films, with annealed films demonstrating a different conduction mechanism than their unannealed counterparts, along with significant improvement in the leakage current and barrier height. This kind of analyses will help optimize the process conditions for Al2O3 deposition and provide an optimal range for device operation, thus improving the reliability of Al2O3 films for applications in CMOS logic and Flash memory.

Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Abstract Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO 3 ) 3 .9H 2 O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al 2 O 3 ). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.

Electric field effects on reduced effective masses of minibands at the mini-Brillouin-zone center and edge in a GaAs/AlAs superlattice

We have investigated the electric-field-strength dependence of the reduced effective masses of the minibands in a GaAs/AlAs superlattice embedded in a p-i-n diode structure with use of electroreflectance spectroscopy. Frantz-Keldysh (FK) oscillations are observed in the energy region between the n = 1 heavy hole to electron transition at the mini-Brillouin-zone center (kz = 0: Γ point) and that at the edge (kz = π/D: π point), where D is the superlattice period. Analyzing the FK oscillations, we evaluate the reduced effective masses at the Γ and π points as a function of electric field strength. The evaluated reduced effective masses are consistent with the values estimated from the calculated miniband dispersion relations in a low electric field regime. It is found that the reduced effective masses tend to be heavier at a given electric field strength. Considering the electric-field-strength dependence of eigenstates calculated using a transfer-matrix method, we conclude that an increase of the reduced effective masses originates from weak localization of the electron envelope function in the transformation process from the miniband to Stark-ladder states in Wannier-Stark localization.

Ruthenium Modified Zr-Doped HfO2 High-k Thin Films with Low Equivalent Oxide Thickness

Thin Zr-doped HfO2 high-k thin film with an equivalent oxide thickness less than 2 nm has been prepared by including ruthenium into the structure. In addition to forming discrete ruthenium nanoparticles in the amorphous Zr-doped HfO2 film, the bulk and interfacial properties, e.g., density of oxygen vacancies and layer composition, were changed with the addition of ruthenium. The permittivity of the film was increased due to the dipole enhancement, which was supported from the frequency-dependent capacitance-voltage and the conductance-voltage measurements change. The ruthenium modified ZrHfO film has a leakage current density 5 orders of magnitude lower than that of the thermally grown SiO2 with the same equivalent oxide thickness. The Schottky emission mechanism was observed in the low electric field regime while the Frenkel-Poole conduction mechanism was applicable in the high electric field regime. A 10-year life expectance is estimated at the gate voltage of 2 V.

Low loss superconducting titanium nitride coplanar waveguide resonators

Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into rf coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e., high and low electric field regimes, respectively. At high field, we found the highest internal quality factors (∼107) were measured for TiN with predominantly a (200)-TiN orientation. The (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, ≈2 nm, layer of SiN during the predeposition procedure. On these surfaces we found a significant increase of Qi for both high and low electric field regimes.

Temperature-dependent low electric field charging of Si nanocrystals embedded withinoxide–nitride–oxide dielectric stacks

In this work we examine the current peaks and the negative differential resistance thatappear in the low electric field regime of oxide–nitride–oxide structures with atwo-dimensional band of silicon nanocrystals embedded in a nitride layer. Thesilicon nanocrystals were synthesized by low energy ion implantation (1 keV,1.5 × 1016 Si+ cm−2) and subsequentthermal annealing (950 °C, 30 min). Electrical examination was performed at temperatures from 20 to100 °C using constant voltage ramp-rate current measurements. This approach enablesus to determine the origin of the observed current peaks as well as to extractthe trapping location of the injected carriers within the dielectric stack. Theresults confirm that the carriers are trapped within the Si nanocrystal band,verifying that this region corresponds to energy minima of the dielectric stack.

Reproducible resistance switching characteristics of hafnium oxide-based nonvolatile memory devices

The resistance switching characteristics of HfO2 thin films deposited by reactive sputtering were examined as a function of the annealing temperature. The results showed that the Pt/HfO2/Pt devices exhibited reversible and steady bistable resistance states [high-resistance state (HRS) and low-resistance state (LRS)]. Reproducible resistance switching from one state to another state or vice versa could be achieved by applying the appropriate voltage bias. The memory performances were related to the crystal structures of the HfO2 films, as confirmed by x-ray diffraction. From current-applied voltage analysis of the devices, LRS in the low electric field regime exhibited Ohmic conduction behavior, while HRS in the high electric field was followed by Poole–Frenkel conduction behavior. The resistance ratios of the two states were maintained in the range of around two orders of magnitude during the endurance test. In addition, it was confirmed that the resistance of the on and off states can be well maintained according to the time elapsed.

Multivalley spin relaxation in the presence of high in-plane electric fields inn-type GaAs quantum wells

Multivalley spin relaxation in $n$-type GaAs quantum wells with in-plane electric field is investigated at high temperature by means of kinetic spin Bloch equation approach. The spin-relaxation time first increases and then decreases with electric field, especially when the temperature is relatively low. We show that $L$ valleys play the role of a ``drain'' of the total spin polarization due to the large spin-orbit coupling in $L$ valleys and the strong $\ensuremath{\Gamma}\text{\ensuremath{-}}L$ intervalley scattering, and thus can enhance spin relaxation of the total system effectively when the in-plane electric field is high. Under electric field, spin precession resulting from the electric-field-induced magnetic field is observed. Meanwhile, due to the strong $\ensuremath{\Gamma}\text{\ensuremath{-}}L$ intervalley scattering as well as the strong inhomogeneous broadening in $L$ valleys, electron spins in $L$ valleys possess almost the same damping rate and precession frequency as those in $\ensuremath{\Gamma}$ valley. This feature still holds when a finite static magnetic field is applied in Voigt configuration, despite that the $g$ factor of $L$ valleys is much larger than that of $\ensuremath{\Gamma}$ valley. Moreover, it is shown that the property of spin precession of the whole system is dominated by electrons in $\ensuremath{\Gamma}$ valley. Temperature, magnetic field, and impurity can affect spin relaxation in low electric-field regime. However, they are shown to have marginal influence in high electric-field regime.

Electrical Characterization of a-C:H as Insulator Material in MIM Structures

a-C:H with low dielectric constant is a very interesting material for applications as inter-metal insulator material in modern ICs, due to the compatibility of deposition process with silicon technology. In this work the fabrication and electrical characterization of Metal- Insulator-Metal structures using a-C:H as the insulating material is presented. The carrier transport mechanisms in high and low electric field regimes are presented. Structures with Ti electrodes show a transport mechanism controlled by the space charge limited current in the low electric field regime, and a Schottky mechanism in the high electric field regime. Preliminary studies in structures with Al electrodes exhibit a different behavior, the transport mechanism does not look like neither Shocktty nor SCL micahnisms. We propose that a-C:H film is an excellent material for inter-metal insulation applications.

Electronic properties of Ge nanocrystals for non volatile memory applications

Charge and discharge phenomena of Germanium nanocrystals fabricated by low pressure chemical vapor deposition are investigated by means of Capacitance–Voltage and capacitance decay measurements. The study shows fast programming and erasing times as compared with conventional devices. It is shown that the charge saturation depends on the gate voltage stress in the low electric field regime. For high gate voltages, a saturation of the stored charge is obtained, indicating that the density of trapped carriers in Ge nanocrystals is limited and depends only on the dots size. Capacitance decay measurements exhibits a very long retention time for holes as compared with silicon nanocrystal memories. This is mainly due to the barrier height for holes at the nc-Ge/ 2 interface. A model for simulation of the retention kinetics has been developed and allows to extract the band alignment of the nc-Ge/SiO2/Si system. The simulation results are then used to determine the band gap energy of Ge nanocrystals. Finally, it is shown that Ge nanocrystals are very good candidates for P-type Metal Oxide Semiconductor nonvolatile memories.

Nonlinear electric conduction in the charge ordering state of (TMTTF)2SbF6

In the charge ordering (CO) state of the quasi-one dimensional conductors (TMTTF) 2 SbF 6 , we measured the current-voltage relations by the pulse current method at ambient pressure. From the measurement, we found that the conductivity is constant at low electric field regime and increases with field above a certain field. It is similar to the nonlinear conduction due to the ordinary density wave (DW) sliding. However, the magnitude of the threshold electric field was larger than that in the DW system. We will discuss the origin of the non-linear electric conduction in the CO state of (TMTTF) 2 SbF 6 and the apparent similarity with it by the DW sliding.

Possible transition from space-charge-limited to injection-limited conduction in poly(3-hexylthiophene) thin films

Abstract Two-terminal thin films of poly(3-hexylthiophene) (P3HT) with a wide electrode separation (150 μ m) has been studied using current–voltage characteristics at different temperatures. Space-charge-limited conduction (SCLC) with high injection barriers (1.3 eV) has been observed at all temperatures in the low electric field regime. A possible transition from SCLC to injection-limited conduction (ILC) is reported. The experimental results have been compared with the disorder-controlled injection model proposed by Arkhipov et al. [V.I. Arkhipov, H. von Seggern, E.V. Emilianova, Appl. Phys. Lett. 83 (2003) 5074; V.I. Arkhipov, E.V. Emilianova, Y.-H. Tak, H. Bassler, J. Appl. Phys. 84 (1998) 848; V.I. Arkhipov, U. Wolf, H. Bassler, Phys. Rev. B 59 (1999) 7514].

Study of velocity field characteristics in pseudomorphic Si 0.8Ge 0.2 p-channel metal-oxide-semiconductor field effect transistor

In this work we report on the enhanced mobility and high electric field characteristics of SiGe p-channel MOSFETs. In the low electric field regime, the devices exhibit effective mobility three times greater than comparable standard Si devices. To determine accurate hole transport characteristics, an analytical modelling of these devices is implemented that takes into account the source drain resistance and short channel effects.

Photocurrent spectroscopy in n-i-n [formula omitted] short period superlattice

Photocurrent spectra of a 50 Å period superlattice (SL) of GaAs Al .3Ga .7As , were measured in the range 14–300 K in a low electric field regime. The energy gap between the heavy-hole and electron extended states of the SL shows the same dependence on temperature as its bulk components. The decrease of photocurrent in the range 100–300 K indicates transport in the extended states of the SL. Different photo-ionization of DX centres existing in the n-doped layers of Al .3Ga .7As causes an effective asymmetry in the n-i-n structure.

Evaluation of the steady‐state photocarrier grating technique with respect to A‐Si: H and its application to A‐Si1–X GeX: H alloys

AbstractThe steady‐state photocarrier grating technique is analysed with respect to deviations from local charge neutrality. We present a generalized expression for the normalized photoresponse β as a function of the grating period as well as of the external electric field; the transport is characterized in the sense of bipolar and ambipolar, diffusion and drift displacement, respectively. Experimental data for undoped a‐Si: H, especially the variation of the β coefficient with the external electric field, are discussed and fitted by the generalized equation. the effective dielectric relaxation time, which takes the trapped photogenerated majority carriers into account, is found to be responsible for ambipolar transport in undoped a‐Si: H in the low electric field regime. Further, the μτ‐products of electrons and holes in a‐Si1‐x Gex: H alloys are deduced experimentally. the low‐gap alloys are an appropriate candidate for photovoltaic applications.

Enhancement of electric field-induced refractive-index variation in a (GaInAsP)(InAs)/InP asymmetric multiple-quantum-film (MQF) structure

The authors report the field-induced refractive-index variation in (GaInAsP)/InP asymmetric quantum-film structures. An enhancement of an electric field-induced refractive-index variation due to the quantum confined Stark effect was theoretically found in the GaInAsP-InAs/InP asymmetric quantum-film structure, especially in a low electric-field regime. Almost two times higher sensitivity was experimentally confirmed in a 40-period GaInAsP (8 nm)-InAs (0.3-0.6 nm)/InP (8 nm) asymmetric multiple quantum-film (MQF) structure in comparison with a symmetric one without an InAs layer at an applied electric field less than 6 V/ mu m. >

Reply to ‘‘Comment on ‘Noncontact doping level determination in GaAs using photoreflectance spectroscopy’ ’’ [J. Appl. Phys. 6 2, 4558 (1987)

Compliance to the low electric field regime necessary for application of the third derivative functional form formalism is demonstrated for ion-implanted samples used to determine the doping level by photoreflectance spectroscopy. Due to field and doping inhomogeneity, the proper line shape is speculated to be described by a superposition of Franz–Keldysh oscillations.